1. Field of Invention
The present general inventive concept relates to tire building equipment, and more particularly, to a tire building drum useful in the assembly of a tire component for subsequent use in the assembly of a tire.
2. Description of the Related Art
The manufacture of a vehicle tire commonly includes the steps of forming a tire carcass, forming a belt and tread portion of the tire separately of the carcass, and thereafter marrying the belt and tread portion of the tire to the carcass to form a “green” tire. The green tire is thereafter treated to form the tread and various other features of the tire.
Formation of the various portions of a tire is typically accomplished using one or more tire building drums of the type defining a cylindrical working surface. For example, formation of the belt and tread portion of the tire is typically accomplished on a type of tire building drum commonly referred to as a “belt and tread drum.” Such a drum has an outer cylindrical surface, or circumference, about which one or more layers of tire belt material (such as, for example, reinforcement cords embedded in a polymeric binder) are laid. Subsequent to laying down the tire belt material, the tire belt material is overlaid with one or more layers of strip tread material to comprise a “belt and tread package.” The circumference of a belt and tread drum is preferably capable of expanding and contracting in order to, for example, accommodate the removal of a completed belt and tread package (which is essentially nonexpandable radially) from the drum circumference and to enable a single drum to be used to form belt and tread packages of alternative diameters. For example, the circumference of a belt and tread drum can be collectively comprised of a plurality of rigid arcuate segments, wherein each segment provides a portion of the cylindrical surface of the drum and is mounted for movement toward and away from the longitudinal axis of the drum to accommodate expansion and contraction of the drum circumference.
A tire carcass is formed on another type of tire building drum, known as a “carcass drum,” in a manner somewhat similar to the forming of a belt and tread package discussed above. Thus, a carcass drum used in forming a tire carcass may also be expandable and contractible as described above. After the tire carcass has been formed, it may be transferred, using a type of tire building drum known as a “transfer ring,” to a second stage tire building drum. On the second stage drum, the tire carcass is held while a transfer ring is used to transfer a belt and tread package from a belt and tread drum onto the outer circumference of the tire carcass. Thereafter, the belt and tread package is married to the carcass. A commonly employed transfer ring may be considered as an inverted belt and tread drum. That is, whereas the outer circumference of a belt and tread drum is adjustable to accommodate the formation of the belt and tread package thereon and to permit the removal therefrom of a completed belt and tread package, a transfer ring defines an inner circumferential surface that is adjustable in diameter to permit the transfer ring to encompass the outer circumference of the belt and tread package and contract in diameter to cause the segments of the transfer ring to engage and grasp the belt and tread package to allow transfer of the package to the carcass of the tire.
Prior art tire building drums of the type described above typically include devices for moving the circumference-defining segments of the drum toward and away from the longitudinal axis of the drum to accommodate adjustment of the diameter of the drum circumference. For example, such devices may comprise one or more cam elements which slidably engage radially-extending guides provided on axially-movable structures at the opposite longitudinal ends of the drum, such that the cam elements are slidable with respect to the drum centerline along the radially-extending guides. These cam elements are, in turn, secured in relation to inner surfaces of the circumference-defining segments of the drum. At least one of the axially-movable structures defines a tapered shape. Thus, by moving the axially-movable structures toward one another, the cam elements are urged outwardly from the longitudinal centerline of the drum along the radially-extending guides of the axially-movable structures, and the circumference-defining segments are therefore urged outwardly from the longitudinal centerline of the drum. The result is an outward expansion of the working surface of the drum defined by the circumference-defining segments secured in relation to the cam elements. Conversely, by moving the axially-movable structures away from one another, the cam elements and associated circumference-defining segments are drawn inwardly toward the longitudinal centerline of the drum, thereby contracting the working surface of the drum. Examples of this type of tire building drum are described and illustrated in U.S. Pat. No. 5,066,354, issued to Benjamin; U.S. Pat. No. 5,232,542, issued to Norjiri et al.; and U.S. Pat. No. 5,264,068, issued to Masuda.
The above-described prior art devices are limited with respect to the extent to which the circumference-defining segments may be moved. More specifically, the extent to which the circumference-defining segments may be expanded and contracted in the above-described prior art devices is limited by the extent to which each of the cam elements may travel along the radially-extending guides. If one or more of the cam elements travels beyond the distal limits of its associated radially-extending guide, the stability of the associated circumference-defining segment may be compromised, such that a non-uniform circumferential surface of the tire building drum is created, thereby leading to inaccuracies formed within a tire component built upon or engaged by the circumferential surface of the tire building drum. Furthermore, in many prior art tire building drums, the presence of mounting equipment and other structures along the central axis of the tire building drum limits the extent to which the radially-extending guides may extend inwardly toward the central axis of the drum. Thus, in many prior art tire building drums, the radially-extending guides extend from the outer circumference of the tire building drum radially inwardly, but terminate at a partial distance along the radius of the tire building drum. Thus, the above-described prior art tire building drums are typically only capable of radial expansion and contraction within a range of approximately 1.4 to 1.
Certain prior art tire building drums have been developed with the goal of obtaining an increased range of expansion and contraction of the tire building drum. One such prior art tire building drum is described and illustrated in U.S. patent application Ser. No. 13/374,448, filed by Byerley (hereinafter “Byerley”). The tire building drum of Byerley includes a thrust plate and a conical actuator disposed at opposite longitudinal ends of the tire building drum, and a plurality of tapered ramp members arranged in a cylindrical configuration between the thrust plate and actuator, each ramp member being secured to an interior surface of a circumference-defining segment of the drum. Pairs of guide blocks are interposed between the thrust plate and each of the ramp members, and between each of the ramp members and the actuator, with each guide block defining a radially-extending channel which faces an associated guide block. For each pair of radially-extending guide blocks, a linear guide member slidably engages both channels in the pair of guide blocks. Thus, in the Byerley device, each guide block associated with a ramp member may slide in relation to an associated linear guide member, and each linear guide member may slide in relation to an associated guide block secured to either the thrust plate or the actuator. Thus, the effective range of movement of each ramp member in relation to the thrust plate and actuator exceeds the overall length of the associated linear guide member.
In prior art tire building drum devices, tolerances or other such dimensional allowances between mating surfaces of the above-discussed cam elements and associated guide rails may, in some instances, allow the circumference-defining segments of the tire building drum to move slightly in relation to other circumference-defining segments of the drum or in relation to the central axis of the drum. Any such movement of the circumference-defining segments superfluous to the desired expansion and contraction movement of the segments could result in variation of the cylindrical configuration of the circumference-defining segments, thereby resulting in non-uniformity of tires formed using the tire building drum. Thus, superfluous movement of the circumference-defining segments in relation to one another or in relation to the central axis of the drum is generally undesirable.
In light of the above, while devices similar to the above-described tire building drum of Byerley may allow for increased range of expansion and contraction of the circumferential working surface of the drum, such devices may allow superfluous movement of the ramp members and associated circumference-defining segments as a result of additional tolerances interposed between each of the linear guide members and associated pairs of guide blocks. Accordingly, it is desirable to produce a tire building drum having an increased range movement, but which also limits superfluous movement of the circumference-defining segments forming the working surface of the drum throughout expansion and contraction of the drum.